Many different types of faults may occur in a transport network, including continuity errors (e.g. loss of signal), connectivity errors (e.g. trace identifier mismatch), payload type errors (e.g. payload label mismatch), alignment errors (e.g. loss of pointer) and signal degradation. Normally, when a fault occurs, an alarm signal is generated. Transport network management systems can be inundated with alarm signals and these must be analysed in order to determine the relative urgency with which each fault needs attention.
Conventionally, faults are characterised by the type of fault and the size of the signal to which the fault relates. Thus, in an SDH network if a fault is detected in, for example, a traffic signal comprising VC-4 data structures, then a network manager may decide to attend to this fault before attending to a fault in a traffic signal comprising, say, VC-12 data structures, on the basis that the former is a larger data structure that can carry a higher volume of traffic. Alternatively, the network manager may decide to deal with a signal mis-direction (connectivity error) type fault before dealing with a signal degradation type fault.
A perceived problem with this arrangement is that the relative importance of the data carried by the traffic signals is not taken into account. Moreover, network operators are spending relatively large amounts of money on sophisticated fault analysis software and large amounts of time in analysing fault reports. It is therefore desirable to reduce the complexity of identifying priority faults.